1. Field of the Invention
The present invention generally relates to the art of printing machine, and more particularly, to a device for cleaning a blanket mounted around a cylindrical drum of a printing machine.
2. Description of the Prior Art
The lithographic printing system includes a blanket mounted around a cylindrical drum. Such a blanket operates to transfer an image layer of an ink from a press plate onto a print sheet by bearing the image layer of the ink on the outer surface thereof. In more detail, the press plate has a surface some portions of which selected according to an image to be printed are made to be hydrophobic, while the remaining portions of the surface are made to be hydrophilic, so that when the surface is uniformly supplied with an oily ink the surface bears a layer of the ink only at the hydrophobic portions thereof. The press plate may be in a flat form or in a cylindrical form mounted around a cylindrical drum. The blanket mounted around the cylindrical drum is first brought into contact with the press plate subsequent to the supply of ink thereon thereby to pick up the image layer of the ink, and is then brought into contact with a print sheet. When a number of the same press plates are needed for a large quantity of printing as in newspaper printing, the blanket mounted around the cylinder may be used to transfer an image layer of ink from an original press plate to a plurality of duplicate press plates.
Such a blanket needs to be periodically cleaned so that an accumulation of ink, fiber flocks or the like retained on the surface of blanket are removed before the accumulation reaches an allowable limit. The cleaning of the blanket has conventionally been done mostly by hand, using some conventional cleaning tools such as brushes or the like under a supply of a conventional cleaning fluid such as soapy water or the like. Although such manual cleaning is convenient in the sense that it needs no special equipments to be particularly installed in the printing system, it is bound to be a problem because degree of cleaning is not always desirably controlled. Too much brushing at a certain portion of the blanket will cause undesirable wearing of that portion, while insufficient brushing at another portion will cause an early degradation of a part of the blanket which is local but in any event limits the period of operation of the blanket between two successive cleanings.
Conventional cleaning devices for general use such as motor driven brushes or rollers may be used for the cleaning of the blanket thereby to increase the cleaning efficiency and thereby to shorten the time during which the printing machine must be stopped for cleaning. However, the cleaning by these conventional motor driven cleaning devices is still not free from the problem that the cleaning applied to different portions of the blanket is not uniform.
A highly mechanized device for cleaning the blanket mounted around a cylindrical drum of a printing machine is disclosed in U.S. Pat. No. 4,344,361. This device has a mechanism for selectively pressing successive portions of a cloth strip against the blanket when it needs cleaning so that the blanket is applied with a wiping-cleaning action by the cloth strip as the blanket is rotated in contact with the cloth strip. The cloth strip is wetted with a cleaning fluid at the portion thereof pressed against the blanket so as to increase the cleaning effect. The cloth strip is gradually fed to renew the portion thereof rubbed against the blanket as the cloth strip wears in use. In the embodiment shown in this U.S. patent specification, the device is mounted adjacent the cylindrical drum bearing the blanket therearound at a location between a top and a horizontal side portion of the cylindrical drum so that the portion of the cloth strip which is pressed against the blanket faces inclinedly downwardly. It is guessed from such a structure that the cloth strip in the device of this U.S. patent will not be properly wetted with the cleaning fluid as it oozes out downwardly from the cloth strip and flows over the blanket downwardly.